If your payment isn't going through, please first do the following:
Check the validity and balance of your card (the balance on your card should be slightly higher than the amount of payment because different banks have different currency exchange rates)
Try a different browser and clear the cache
Make sure your pop-up windows are enabled
Payment issues may also be connected to particular regulations of your bank. Please don't hesitate to contact firstname.lastname@example.org if you still need assistance.